This invention relates to apparatus and method for sharpening saw blades having planetary motion in transverse cutting and, more particularly, to apparatus and method for transversely cutting continuously moving multi-ply web material such as convolutely wound paper logs, superposed plies, etc. The basic teaching to which this invention applies is co-owned U.S. Pat. No. 4,041,813 and reference may be had thereto for details of construction and operation not set forth herein.
The above-mentioned patent has to do with a continuous motion "CM" saw, viz., the product being cut is moved continuously in contrast to being indexed or stepped. This involved moving a disc blade through a planetary orbit, i.e., one skewed to the transverse cutting plane. During cutting, this advanced the saw along the path of travel of the material being cut, i.e., the convolutely wound log or the like. It will be appreciated that in making toilet tissue or toweling, retail diameter logs are rewound at high speed from a parent roll and then transversely cut to retail length rolls.
Although the "CM" saw of the '813 patent has been commercially available there have been difficulties in sharpening its blades so that the industry has been using intermittent motion saws such as that described in co-owned U.S. Pat. Nos. 4,584,917 and 4,821,613. Such a saw, running at full speed has a constant centrifugal loading of 8.3 g's at a constant direction relative to the grinder. Due to the simple rotary motion of the grinder assembly and the ability to bolt the grinder to a primary rotating machine member, component mass, compactness and resistance to cyclic loading are of little concern during grinder design.
However, a "CM" saw at full speed has a constant centrifugal loading at of 27.3 g's (4 times greater) but a worse problem is that due to the planetary motion the direction of the force is constantly changing relative to the grinder assembly. The force direction inside the grinder moves through 360.degree. during each cycle of product cutting. Each component of the assembly is therefore under fatigue loading being cycled 1/4 million times each day. This is why since the invention of the "CM" saw a grinder has not been found that will reliably hold up and give a high quality grind or hone at the speeds customers demand. Because of the skew angle the unit can only be mounted to the blade spindle housing. This is the only machine member that follows the blades path. This housing is relatively small and should be kept in balance, yet forces the grinders to be cantilever mounted which again is difficult due to the cyclic loading and balancing problems.
Past designs relied on independently bringing in each grinding stone to a set position using a linear (or near linear) motion. My design instead takes both stones and mounts them on a common arm and then using a pivoting motion causes both stones to simultaneously contact the blade and stop at a set position with a single moving part.
The main advantage is a single moving part, since each part that moves is subject to a certain amount of looseness. It's that looseness that gives the cyclic loading a foot hold for causing wear and failure of parts. To then fight wear at the pivot point, the cylinder that causes the pivoting action has enough force capacity to push out all looseness in the pivot joint while operating at up to 45 g's (250 rpm).
Another advantage is less weight because there is now only one moving part to grind in contrast to the prior duplicate independent assemblies. Also the use of less parts reduces the cost.
Still another advantage is the ease of stone adjustment to compensate for blade wear. Normally, a 24" diameter blade will wear down to 18" during its cutting life. This requires the grinding stones to move closer to the blade axis to maintain contact with the blade periphery.
To achieve grinding under these circumstances, the pivoting motion of the stones was applied to a nut and screw. The screw can then be turned to give manual adjustment or with the addition of an indexing system it can be done automatically. The locking system for the screw is necessary for both the manual or automatic arrangements again due to the cyclic loads which may try to turn the screw. Since the screw must turn to give adjustment it is also subject to looseness, but the same cylinder that removes the looseness in the pivoting arm will also remove this radial clearance. The screw is heavily preloaded in the axial direction to also remove that looseness, and the auto adjustment and locking areas include springs that remove looseness from its joints.